1. Field of the Invention
The present invention relates to a lens apparatus in which at least one lens and an aperture stop are moved in an optical axis direction in zooming or focusing, and to an image pickup apparatus provided with the lens apparatus.
2. Description of the Related Art
Image pickup apparatuses such as video cameras or digital still cameras require a lens apparatus capable of achieving a higher zoom magnification and performing focusing on an object at a closer distance while being small in size. As a method for realizing such a lens apparatus, decreasing a minimum distance between lenses that are adjacent to each other in the optical axis direction and relatively movable in that direction is effective.
Japanese Patent Laid-Open Nos. 2004-053633, 2004-258516 and 7-151972 disclose lens apparatuses in which an aperture stop is disposed between lenses that are relatively movable. In these lens apparatuses, it is necessary to decrease a minimum distance between the lenses disposed on both sides of the aperture stop while avoiding interference of the lenses with the aperture stop.
The lens apparatus disclosed in Japanese Patent Laid-Open No. 2004-053633 disposes the aperture stop on an image side further than an object side lens surface of a second lens group (counted from the object side), and thereby decreases the minimum distance between the lenses disposed on the both sides of the aperture stop. However, in this lens apparatus, the aperture stop is moved integrally with the second lens group in zooming. This increases variation of an exit pupil in the zooming, in an image pickup apparatus in which an image sensor (image pickup element) such as a CCD sensor is disposed at an image plane, which is undesirable for the image sensor.
On the other hand, in the lens apparatus disclosed in Japanese Patent Laid-Open No. 2004-258516, the aperture stop is also moved in zooming, which enables suppression of the variation of the exit pupil. Moreover, in the lens apparatus disclosed in Japanese Patent Laid-Open No. 7-151972, the aperture stop is unmoved (fixed) in zooming.
In the lens apparatuses disclosed in Japanese Patent Laid-Open Nos. 2004-258516 and 7-151972, it is necessary to avoid interference of the aperture stop with the lens in a state where they are closest to each other. Therefore, a minimum distance between the aperture stop and the lens is increased, which makes it impossible to sufficiently decrease the minimum distance between the lenses disposed on the both sides of the aperture stop. In particular, in a case where an aperture diameter of the aperture stop is variable, a thickness of a mechanism to vary the aperture diameter further increases the minimum distance between the lenses disposed on the both sides of the aperture stop.
As in the lens apparatus disclosed in Japanese Patent Laid-Open No. 7-151972, fixing the aperture stop in zooming causes a second lens group and a third lens group, which are disposed on an image side further than the aperture stop, to perform variation of magnification. Thus, movable amounts of the second and third lens groups are limited, which makes it difficult to sufficiently correct aberration variation in zooming.